1. Field of the Invention
The invention relates to an illumination device having a good emission distribution property and its manufacturing method.
2. Description of Related Art
Recently, illumination devices using light emitting elements such as light-emitting diode (LED) elements or organic EL elements have been explored to replace illuminating devices using fluorescent tubes. In such illuminating devices, fluorescent material regions that contain a fluorescent material are conventionally provided at the light emitting side of the light emitting elements. Light emitted from the light emitting elements are converted into light having a wavelength that is more favorably felt against human visibility by the fluorescent material contained in the fluorescent material regions and then emitted outside.
For example, Japanese patent Laid-Open No. 10-242513 describes an LED light emitting unit in which a fluorescent material region containing yttrium aluminum garnet phosphor activated with cerium is arranged at the light emitting side of an LED element composed of a nitride compound semiconductor element. In this LED luminescent device, part of the blue light emitted from the LED element is converted into yellow light by the fluorescent material and emitted outside as white light. Illumination devices with an increased luminescent area by providing numbers of such light emitting units that emit white light have also been considered. However, in the illumination device having an increased luminescent area by providing numbers of the above described light emitting units, there has been a problem that it was difficult to obtain an illumination device having a good emission distribution property.
More specifically, in Japanese patent Laid-Open No. 10-242513, the fluorescent material region is formed by curing an epoxy resin in which a (RE1-xSmx)3(AlyGa1-y)5O12:Ce phosphor is scattered. However, in such a method that cures a resin material in which a fluorescent material is scattered, concentration of the fluorescent material varies for example because the fluorescent material sinks during the curing due to the difference of gravities between the fluorescent material and the resin material. The degree of variation also differs depending on the time from the preparation of the resin material in which a fluorescent material is scattered until the resin material is cured. Therefore, distribution and concentration of the fluorescent material in the formed fluorescent material regions tend to vary. In addition, it is difficult to make the amount of the resin material provided at the light emitting side of the LED element in which the fluorescent material is scattered uniform. As such, it was difficult to manufacture light emitting units having a desired color with good repeatability.
In an illumination device with an increased luminescent area by providing numbers of such light emitting units composed of a light emitting element and a fluorescent material region, as described above, the emission property of the light emitted from respective light emitting units such as its color varies because of the variation of concentration and distribution of the fluorescent material within the respective fluorescent material regions, and as a result, there was a problem that it was difficult to obtain an illumination device with a good emission distribution property.